1. Field of the Invention
The present invention relates to an electromagnetic wave shielding member using a mesh consisting of a thin metal film (also known as “metal foil”) and a process for producing the same.
More specifically, the present invention relates to an electromagnetic wave shielding member using a mesh consisting of a thin metal film, for shielding electromagnetic waves generated from electromagnetic wave sources, such as electronic tubes of displays, which electromagnetic wave shielding member has see-through properties and electromagnetic wave shielding properties and, at the same time, is free from a change in color of an adhesive upon etching at the time of the formation of the mesh, is improved in etchability, and can withstand etching at the time of the formation of the mesh. The present invention also relates to an electromagnetic wave shielding member which can improve contrast and can realize good visibility. Further, the present invention relates to an electromagnetic wave shielding member which, according to need, can cut or absorb near-infrared radiation (light) generated from the inside of displays and can absorb specific wavelengths, i.e., the wavelengths of external light-derived visible light and/or near-infrared radiation (light) to improve contrast and can realize good visibility.
2. Prior Art
From the viewpoint of a harmful effect of electromagnetic waves on the human body, lowering the emission intensity of electromagnetic waves to values satisfying specifications has hitherto been required of electronic devices, which generate electromagnetic waves and, in use, are accessed directly by a person, for example, electronic tubes of displays, for example, plasma displays.
Further, in plasma display panels (hereinafter referred to also as “PDPs”), since plasma discharge is utilized for light emission, unnecessary electromagnetic waves in the frequency band range of 30 to 130 MHz are leaked outside the plasma display panels. For this reason, minimizing electromagnetic waves is required from the viewpoint of avoiding a harmful effect on other equipment (for example, information processing devices).
To cope with these demands, electromagnetic wave shields, wherein the outer periphery of electronic devices or the like, which generate electromagnetic waves, is covered with a suitable conductive member, are generally adopted for removing or attenuating electromagnetic waves that flow out from electronic devices, which generate electromagnetic waves, to the outside of the devices.
In display panels such as PDPs, it is common practice to provide an electromagnetic wave shielding plate having good see-through properties in front of a display.
The fundamental structure per se of electromagnetic wave shielding plates is relatively simple, and examples of conventional electromagnetic wave shielding plates include: an electromagnetic wave shielding plate wherein a thin transparent conductive film, such as a thin indium-tin oxide film (hereinafter referred to also as “ITO film”), has been formed by vapor deposition on the surface of a transparent glass or plastic substrate, sputtering or the like; an electromagnetic wave shielding plate wherein, for example, a suitable metallic screen, such as a wire mesh, has been applied to the surface of a transparent glass or plastic substrate; and an electromagnetic wave shielding plate wherein a fine mesh consisting of a thin metal film has been provided on the surface of a transparent glass or plastic substrate by forming a thin metal film on the whole surface of the substrate, for example, by electroless plating or vapor deposition and treating the thin metal film by photolithography or the like.
The electromagnetic wave shielding plate comprising an ITO film provided on a transparent substrate has excellent transparency and generally has a light transmittance of about 90%. Further, since an even film can be formed on the whole surface of the substrate, when the electromagnetic wave shielding plate is used in displays or the like, there is no fear of causing moiré or the like attributable to the electromagnetic wave shielding plate.
In the electromagnetic wave shielding plate comprising an ITO film provided on a transparent substrate, however, since a vapor deposition or sputtering technique is used for the formation of the ITO film, the production apparatus used is expensive. Further, the productivity is generally poor. This poses a problem that the price of the electromagnetic wave shielding plate per se as a product is high.
Further, the electromagnetic wave shielding plate comprising an ITO film provided on a transparent substrate has at least one order inferior electrical conductivity as compared with the electromagnetic wave shielding plate provided with a mesh consisting of a thin metal film. Therefore, this electromagnetic wave shielding plate is effective for objects which emit relatively weak electromagnetic waves, but on the other hand, when used in objects which emit strong electromagnetic waves, the shielding function is unsatisfactory posing a problem that electromagnetic waves are leaked and, in some cases, the specifications cannot be satisfied.
In the electromagnetic wave shielding plate comprising an ITO film provided on a transparent substrate, increasing the thickness of the ITO film can improve the electrical conductivity to some extent. In this case, however, disadvantageously, the transparency is remarkably deteriorated. In addition, a further increased thickness incurs a further increased product cost.
The electromagnetic wave shielding plate comprising a metallic screen applied onto the surface of a transparent glass or plastic substrate or the application of a suitable metallic screen, such as a wire mesh, directly onto the surface of a display is simple and is low in cost. This, however, suffers from a serious drawback that, since the light transmittance of a metallic screen having an effective mesh size (100 to 200 mesh) is not more than 50%, the display is very dark.
In the case of the electromagnetic wave shielding plate comprising a mesh consisting of a thin metal film provided on the surface of a transparent glass or plastic substrate, since the external form is shaped by etching according to photolithography, a fine, high open area ratio (high light transmittance) mesh can be prepared. Further, since the mesh consists of a thin metal film, the electrical conductivity is much higher than that of the ITO film or the like. This offers an advantage that strong emitted electromagnetic waves can be shielded.
This electromagnetic wave shielding plate, however, cannot absorb the reflection of external light from the display panel and has poor visibility and, in addition, suffers from an unavoidable problem that the production process is troublesome and complicate and the productivity is low resulting in high production cost.
Thus, the electromagnetic wave shielding plates have respective advantages and disadvantages, and, in use, a suitable electromagnetic wave shielding plate is selected according to applications. Among the above electromagnetic wave shielding plates, the electromagnetic wave shielding plate comprising a mesh consisting of a thin metal film provided on the surface of a transparent glass or plastic substrate has good electromagnetic wave shielding properties and light transmission properties and has recently become used for electromagnetic wave shielding purposes in such a manner that the electromagnetic wave shielding plate is placed in front of display panels such as PDPs.
In the conventional electromagnetic wave shielding plates and displays, a feature, which cuts off or absorbs near-infrared radiation (light) emitted from the inside of the display and can absorb specific wavelengths, i.e., the wavelengths of visible light emitted from the inside of the display or derived from external light for improving the contrast, is stacked by a separate step, for preventing malfunction of other equipment. Therefore, disadvantageously, the process is troublesome, the productivity is poor, and the thickness is large.
An electromagnetic wave shielding member comprising a mesh consisting of a thin metal film provided on the surface of a transparent glass or plastic substrate is shown in FIG. 4. This electromagnetic wave shielding member will be briefly described.
FIG. 4A is a plan view showing an electromagnetic wave shielding member, FIG. 4B a cross-sectional view taken on line A1–A2 of FIG. 4A, and FIG. 4C an enlarged view of a part of a mesh portion.
In FIGS. 4A and 4C, direction X and direction Y are indicated for the clarification of the positional relationship and mesh shape.
The electromagnetic wave shielding member shown in FIGS. 4A to 4C is an electromagnetic wave shielding member for an electromagnetic wave shielding plate which, in use, is placed in front of displays such as PDPs. In this electromagnetic wave shielding member, a grounding frame portion and a mesh portion are provided on one side of a transparent substrate. The grounding frame portion 415 is formed of the same thin metal film as the mesh portion and is provided around the periphery of the mesh portion 410 so as to surround the screen region of the display in using the electromagnetic wave shielding plate in such a manner that the electromagnetic wave shielding plate is placed in front of a display.
As shown in FIG. 4C (a partially enlarged view of the mesh portion 410), the mesh portion 410 comprises a group of a plurality of lines 470 provided parallel to each other at a predetermined pitch Px in direction Y and a group of a plurality of lines 450 provided parallel to each other at a predetermined pitch Py in direction X. In this connection, it should be noted that the shape of the mesh is not limited to that shown in FIG. 4.
FIG. 5A shows an example of the case where an electromagnetic wave shielding plate 500 using the electromagnetic wave shielding member shown in FIG. 4 is used in such a state that the electromagnetic wave shielding plate 500 is placed in front of PDP, and FIG. 5B an enlarged cross-sectional view of an electromagnetic wave shielding region (corresponding to portion B0) shown in FIG. 5A.
As shown in FIG. 5B, the electromagnetic wave shielding region (corresponding to portion B0) in the electromagnetic wave shielding plate 500 comprises, provided on the viewer side of a transparent glass substrate 510, an NIR layer (a near-infrared absorption layer) 530, an electromagnetic wave shielding member 400 shown in FIG. 4, and a first AR layer (an antireflection layer) film 540 in that order as viewed from the transparent glass substrate and, on the PDP 570 side of the transparent glass substrate 510, a second AR layer (an antireflection layer) film 520.
In FIG. 5, numeral 500 designates a front plate for display, numeral 400 an electromagnetic wave shielding member, numeral 410 a mesh portion, numeral 430 a transparent substrate, numeral 510 a glass substrate, numeral 520 a second AR layer film, numeral 521 a film, numeral 523 a hardcoat, numeral 525 an AR layer (an antireflection layer), numeral 527 an antifouling layer, numeral 530 an NIR layer (an near-infrared absorption layer), numeral 540 a first AR layer film, numeral 541 a film, numeral 543 a hardcoat, numeral 545 an AR layer (an antireflection layer), numeral 547 an antifouling layer, numerals 551, 553, and 555 each an adhesive layer, numeral 570 PDP (a plasma display), numeral 571 an attachment boss, numeral 573 a screw, numeral 572 a pedestal, numeral 574 a mounting bracket, numeral 575 the front part of a housing, numeral 576 the rear part of a housing, and numeral 577 a housing. The position of the NIR layer (near-infrared absorption layer) and the position of the electromagnetic wave shielding member are not particularly limited to those shown in FIG. 5B. Further, if necessary, a colored layer for color regulation may be provided.
The use of an adhesive comprising an ethylene-vinyl acetate copolymer has been proposed as a method for bonding an electromagnetic wave shielding member to a transparent substrate (Japanese Patent Laid-Open No. 307988/1999). In particular, it is known that high adhesive strength and transparency are required of the adhesive for electromagnetic wave shielding members for displays. Since, however, the adhesive is not resistant to etching at the time of the formation of a mesh, the color of the adhesive is disadvantageously changed.